Robi

Robi

Robi

Have any particulars on your combination?  As you mention, your combination may be marginal for pump gas.

Your basic ignition timing adjustments should be made with the vacuum advance unhooked.  Using a dial back timing light can also be a problem as many of these vary in the timing readings they put out.  The older MSD instruction sheets use to be specific in what timing lights were recommended for ignition timing adjustments and there were no dial back timing lights on that list.

When you say you have 39° timing at 2500 rpms, does this mean that all the timing is in at 2500 rpms or that’s just where you’re setting the total?  If the timing is continuing to increase after 2500 rpms, then the total timing ideally needs to be set at an rpm point just above where the mechanical advance in the distributor is pegged out.  But that brings up another point.  Previous experience has shown that having the total timing in at 2500 rpms is likely too low.  For the EMC engine, I found that a lazy curve with the total timing coming in at 3400 rpms made more power in that particular instance.

I had a stroker Y on the dyno yesterday that had been simply timed with the initial settings and raced that way.  It has a stock distributor with an electronic conversion.  The total timing on that engine came in at 4700 rpms and was 26°.  Made 274 HP.  Kept bumping up the timing in increments and with each increase was rewarded with a HP increase.  The same engine was making 306 HP at 38° total and this is a pump gas engine.  The only problem is increasing the timing also leans the fuel mixture and in this particular case, the engine has a 3X2 setup with the Holley 94’s.  The jetting was already on the lean side before adding additional advance to the ignition.  There’s an easy 15-20 HP left on the table in this instance by not jetting the engine up fatter.  Because a single four intake and Holley carb will be on the engine when it leaves the shop Monday, there was no time wasted in tinkering with the jetting on the 3X2 setup.

Robi

Does your timing light have a knob on its backside for timing curve adjustments?  If so, then that will be a 'dial back' light.  With the MSD spring kit, the lightest springs typically has the timing all in at 2500 rpms.   Any other spring combination of springs should have the total timing coming in at a higher rpm.  Putting the original stiff heavy silver springs back in and working backwards from there would be a good starting point.  Runing the engine at less than optimum ignition timing will not be detrimental to the the engine other than making for some additional heat that must be carried away by the cooling system.

Robi

Your timing light sounds like a modern equivalent of the ‘dial back’ lights to which I'm referring.  I’ll suggest borrowing a conventional timing light and comparing the timing reading against yours at both idle and with the engine sped up to where the total timing is in.

Robi

The MSD instructions give distributor advance in crankshaft degrees while all the old manuals give advance in distributor degrees and are doubled for crankshaft degrees.

We used the 2 blue springs and blue bushing on our recent build and it worked well.

If you are monitoring air fuel ratio with an O2 sensor it will need to read a little richer than if the engine is on a dyno with air hat and fuel turbine readings. On a SuperFlow dyno the best power is found around 13.5-14.5:1. We have run some Y-Blocks in the 15:1 range and they'll still make power but these are not O2 readings.

I would guess that O2 readings should be 12.0 to 13.0:1. 

Limiting the vacuum advance to an additional 10 is a good idea.

Robi